Jubilee crankshaft seal.

I removed the clutch basket to replace the crankshaft seal. Before I took the clutch apart I loosened the clutch nut by jamming a brass drift between the chain and the primary sprocket as there is no way to stop the clutch spinning when the chain is off. At least I did not find a way. The alternator stator can be difficult to remove but when that is out of the way the primary sprocket and clutch basket and chain should all come off together. You may find the crank seal has been peened in place. If so, remove any burrs before fitting the new seal. My seal came out easily but  I have heard that if it is difficult to remove, screw in a self-tapping screw at the outer edge and use mole grips to pull out the seal. Be careful not to damage the seal housing.

Dennis 

John,

Your comments about bolt removal will sound odd to most lightweight owners.

The very first lightweights had a steel primary chain slipper attached by two allen screws. If there is oil in the crankcase, it will flow out when you remove the screws as you describe. Both threaded holes break through the crankcase wall.

Norton/AMC noticed very quickly that owners/dealers were setting the primary chain too tight. The aluminium crankcase expanded more than the steel duplex chain at temperature. Chain became too tight and clutch/main bearings were overloaded.

Lightweights made later had two studs to fix a nylon slipper block. Using the same holes in the crankcase. It is not necessary to remove these studs, even when removing the primary chaincase inner. So no oil escapes from the crankcase. When the owner sets the primary chain tension too tight, the nylon block wears away or it moves before damage is done to bearings.

Anyone worried about oil leakage from crankcase to primary drive through the stud or bolt threads could use a nutlock/thread sealer on assembly. IMHO the leakage through these two unsealed threads should be insignificant compared to the contents of the primary case. 

Peter